Conventionally, paper has been popularly used for printing various contents (hereinafter, referred to as printed contents). Printing paper carrying printed contents often has a high value particularly when it is used to operate as a medium of exchange for commercial goods such as paper money, as a medium of certification of contents such as certificates, as a medium of storing information such as personal works and as other mediums.
Therefore, various measures have been proposed to prevent unauthorized copying of printed contents that are printed on printing paper. Such measures include a technique of burying micro IC (integrated circuit) chips in generally available paper (to be referred to as plain paper hereinafter) and a technique of preparing special paper by specially processing ordinary paper (see, Patent Reference 1)
Patent Reference Japanese Patent Application Laid-Open Publication No. 2000-352913.
However, known measures including the above cited ones involve the use of a cumbersome technique and an operation of printing contents in limited premises to make it difficult to prevent unauthorized copying of printed contents particularly when original printing paper is prepared by printing the contents on paper that is available in ordinary homes and offices. Then, there arises a problem that printed contents printed on printing paper can hardly be protected properly.